Research On Low Delay Technology For Mobile Fronthaul Optical Access Network

With the continuous improvement of people's pursuit of work and entertainment methods and content,business fields such as network live broadcast,augmented reality,virtual reality and cloud computing are very popular,which also puts forward high requirements for the bandwidth and delay of 5g mobile communication network.Among them,after functional reconfiguration,mobile fronthaul not only requires large capacity,but also puts forward strict requirements of 100μs level for delay.In order to reduce the deployment and maintenance costs of the fronthaul and improve the transmission capacity of fronthaul,the industry hopes to introduce Ethernet technology into the fronthaul.However,Ethernet follows the best effort transmission mode.When it is applied to mobile fronthaul,it will bring intolerable delay and delay jitter to fronthaul at the switching node because of the flow aggregation mechanism.In order to reduce the transmission delay and delay jitter of the Ethernet based fronthaul,this paper studies the flow aggregation algorithm at the switch node in the fronthaul.The flow aggregation scheme based on time window can effectively reduce the transmission delay of new traffic without causing delay jitter to the through traffic.However,when the network load is large,the effect of this scheme will be significantly reduced.Based on the analysis and improvement of the existing schemes,this paper proposes an Location-Load based Asynchronous Aggregation Scheme(LL-AAS).The scheme uses the properties of link load and device location in fronthaul to reduce the probability of blocking the forward traffic by adjusting the frame length of the Ethernet frame encapsulated by the forward traffic at different locations.In order to verify the feasibility of the proposed scheme,a flow aggregation simulation system based on the time axis is designed and constructed,and the proposed scheme is verified by simulation.The simulation results show that LL-AAS can effectively reduce the delay and jitter caused by the aggregation of the previous network flows.In order to overcome the problem of low transmission efficiency and poor scalability in LL-AAS,an Adaptive Frame Size Time Window(AFS-TW)aggregation scheme is proposed.By monitoring and feedback the network load,this scheme adjusts the package length of the fronthaul traffic in real time,and pursues the most efficient flow aggregation effect.The simulation results show that the scheme can reduce both the encapsulation cost of the fronthaul traffic and the transmission delay.In the flow aggregation scheme based on frame preemption,high priority traffic will inevitably be introduced into delay jitter.In order to eliminate the delay jitter caused by the frame preemption mechanism,this paper proposes a frame preemption aggregation scheme with fixed delay.By applying a fixed delay to the through traffic,the scheme can form a buffer time window which can predict the demand of frame preemption and avoid the blocking problem caused by frame preemption segmentation operation.The simulation results show that the scheme can guarantee the transmission delay of new traffic is very low and eliminate the delay jitter introduced by the original scheme to the direct traffic.